The present invention relates to a method of producing a modified polyolefin serving as a compatibilizer for various resin compositions, and particularly to a method of producing a modified polyolefin suffering from only small decrease in a molecular weight in the course of graft polymerization and having a high graft ratio.
Since the polyolefin resins such as polypropylene, polyethylene and olefinic elastomers are low in costs and have excellent moldability, insulation, chemical resistance, mechanical strength, etc., they can be used in various applications such as films, fibers, molded articles, etc.
However, since the polyolefin resins consisting of non-polar molecules have poor compatibility with such other resins as nylons, polyesters, polycarbonates having strong polarities, the blends of these polyolefins with such other resins fail to provide molded products with sufficiently good appearance and mechanical properties.
Also, the polyolefin resins are poor in chemical properties such as adhesion, paintability, printability, hydrophilic nature, etc. due to their chemical structures. Accordingly, an extensive research has been conducted to improve such properties by graft-polymerizing the polyolefin resins with various unsaturated compound monomers.
Japanese Patent Laid-Open No. 50-52156 discloses a method of producing a modified polyolefin composition comprising melt-blending a propylene-based polyolefin, a polar vinyl monomer, a radical generator and a microporous filler at a temperature higher than a decomposition temperature of the radical generator.
Japanese Patent Laid-Open No. 52-105993 discloses a method of producing a modified polypropylene comprising reacting polypropylene, a liquid rubber and maleic anhydride in a solvent by using a radical generator.
Japanese Patent Laid-Open No. 55-50040 discloses a method of producing a modified polypropylene having a maleic acid graft content of 1-15 weight %, comprising reacting polypropylene, rubber and maleic anhydride in the absence of a solvent by using a radical generator.
Japanese Patent Laid-Open No. 58-67743 discloses a modified polypropylene composition comprising a modified polypropylene, a part or whole of which is grafted with unsaturated carboxylic acid, a cross-linking agent and an organic peroxide having a one-minute half-life temperature 10.degree. C. or more higher than the melting point of the modified polypropylene.
Further, Japanese Patent Laid-Open No. 1-236214 discloses a method of producing a modified polyolefin resin composition comprising the step of blending in a molten state a mixture of (A) 100 parts by weight of a polyolefin resin having a melt flow rate of 0.05-60 g/10 minutes, (B) 0.1-5 parts by weight of at least one compound selected from an unsaturated carboxylic acid, its derivative and an epoxy monomer, (C) 0.1-5 parts by weight of an unsaturated aromatic monomer, and (D) 0.01-2 parts by weight of a radical generator, a molar ratio of (B)/(C) being 0.1 and more and less than 1.
Also, various graft polymerization methods of polyethylene with unsaturated carboxylic acids are disclosed, for instance, in Japanese Patent Laid-Open Nos. 50-4189, 51-122152, 52-25845 and 57-165413.
However, in these methods of producing modified polyolefins, since a decomposition reaction also takes place in the main chain of the polyolefins in the course of the graft reaction, only modified polyolefins having low molecular weights can be obtained. Besides, the graft monomers such as maleic anhydride, etc. have a sublimation property and generate an unpleasant odor, making it difficult to handle them at melt reaction. In addition, the resulting modified polyolefins suffer from discoloration such as yellowish coloring. Further, since the modified polyolefins obtained by the above methods fail to have a sufficiently high graft ratio of maleic anhydride, etc., they are unsatisfactory as compatibilizers.
In order to overcome these problems, attempts have been made to use as a modifying monomer glycidyl methacrylate, etc. containing an epoxy group in place of the maleic anhydride. However, since the glycidyl methacrylate is in the form of a liquid, its handling is difficult at a melt reaction. It also generates an unpleasant odor and suffers from discoloration and poor reaction efficiency.